Implement being able to drop through soft platforms (#64)

Reviewed-on: #64
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/state/platform_pass.rs

@@ -0,0 +1,61 @@
+use super::{CollisionContext, EnterContext, FighterStateImpl, InterruptContext, UpdateContext};
+use crate::fighter::animation::AnimKind;
+use crate::fighter::state::air::AirborneStateCommon;
+use crate::fighter::state::{ExitContext, FighterState, air, jump};
+
+#[derive(Debug, Clone, Copy, Hash, Default)]
+pub struct PlatformPassState {
+    airborne_state_common: AirborneStateCommon,
+    ignored_polygon: usize,
+}
+
+impl PlatformPassState {
+    pub fn new(airborne_state_common: AirborneStateCommon, ignored_polygon: usize) -> Self {
+        Self {
+            airborne_state_common,
+            ignored_polygon
+        }
+    }
+}
+
+impl FighterStateImpl for PlatformPassState {
+    const NAME: &'static str = "PlatformPass";
+    
+    fn check_interrupt(&self, state_context: &mut InterruptContext) -> Option<FighterState> {
+        jump::check_input_double_jump(state_context)
+    }
+
+    fn on_enter(&mut self, state_context: &mut EnterContext) {
+        state_context.surface.ignore_polygon(self.ignored_polygon, state_context.game_settings.fighter_common.platform_pass_platform_ignore_duration_frames);
+        state_context.velocity.y = state_context.game_settings.fighter_common.platform_pass_initial_downwards_velocity;
+        state_context.play_animation(AnimKind::PlatformPass, false);
+    }
+
+    fn on_exit(&mut self, state_context: &mut ExitContext) {
+        state_context.surface.clear_polygon_ignore(self.ignored_polygon);
+    }
+
+    fn update(&mut self, state_context: &mut UpdateContext) {
+        air::update_standard_motion(state_context, &mut self.airborne_state_common);
+    }
+
+    fn check_collision_interrupt(
+        &mut self,
+        state_context: &mut CollisionContext,
+    ) -> Option<FighterState> {
+        air::collision_interrupt(
+            state_context,
+            crate::fighter::state::land::LandingType::Normal,
+        )
+    }
+    
+    fn is_visually_grounded<'a>(
+        &'a self,
+    ) -> bool {
+        false
+    }
+
+    fn surface_policy(&self) -> super::SurfacePolicy {
+        super::SurfacePolicy::Airborne(crate::fighter::surface::EcbLockPolicy::StartOnDetach)
+    }
+}